请教个SQL递归求和的问题

create table test(

NAME varchar2(20), P_NAME varchar2(20), NUM int);



insert into test values('a','-1',3 );

insert into test values('b','-1',4 );

insert into test values('c','a',5 );

insert into test values('d','b',6 );

insert into test values('e','c',7 );

insert into test values('f','d',8 );

insert into test values('g','e',9 );

COMMIT;

SELECT NAME, P_NAME, SUM(NUM) num

  FROM (SELECT NUM, CONNECT_BY_ROOT NAME NAME, CONNECT_BY_ROOT P_NAME P_NAME

          FROM TEST S

        CONNECT BY PRIOR NAME = P_NAME

         START WITH P_NAME = '-1')

 GROUP BY NAME, P_NAME;

 输出:

NAME	P_NAME	NUM

b	    -1	    18

a	    -1	    24

select 

    NAME,P_NAME, 

    (select sum(NUM) from t connect by P_NAME = prior NAME start with NAME= t0.NAME) NUM

from 

    t t0 

where 

    P_NAME=-1;